Meiosis is a fundamental process for all sexual reproducing organisms. Problems in this process can lead to chromosome mis-segregation, which can result in sterility, lethality, and diseases such as Down's syndrome. Many proteins and elements of meiosis are evolutionarily conserved, there is species level variation in the precise meiotic mechanisms, but there is remarkably little data on how these different mechanisms or the associated proteins have evolved. I propose to address the question of how a novel meiotic process and associated proteins evolve by studying cytological and functional molecular genetic differences between closely related diploid and autotetraploid Arabidopsis arenosa. Polyploidy is an ideal system to study this question, because there is strong selective pressure on the meiosis machinery to ensure proper pairing, crossing- over, and segregation in an environment with double the number of homologous chromosomes. To catalogue the differences between these environments, I propose to conduct a detailed cytological investigation of diploid, natural autotetraploid, and synthetic tetraploid lines. I will also investigate the function of meiosis related proteins with strong signatures of selection in the tetraploid lineage through transgenic analysis. In a complimentary experiment, I will conduct an artificial selection experiment on gamete viability in the synthetic autotetraploid and genetically map loci that ensure proper meiosis in the tetraploid.